There are three major isoforms of the human membrane folate binding proteins, α, β and γ. The α and β isoforms have about 70% amino acid sequence homology and differ dramatically in their stereospecificity for some folates. Both isoforms are expressed in both fetal and adult tissue, although normal tissue generally expresses low to moderate amounts of FR-β. FR-α, however, is expressed in a subset of normal epithelial cells, and is frequently strikingly elevated in a variety of carcinomas (Ross et al. (1994) Cancer 73(9):2432-2443; Rettig et al. (1988) Proc. Natl. Acad. Sci. USA 85:3110-3114; Campbell et al. (1991) Cancer Res. 51:5329-5338; Coney et al. (1991) Cancer Res. 51:6125-6132; Weitman et al. (1992) Cancer Res. 52:3396-3401; Garin-Chesa et al. (1993) Am. J. Pathol. 142:557-567; Holm et al. (1994) APMIS 102:413-419; Franklin et al. (1994) Int. J. Cancer 8 (Suppl.):89-95; Miotti et al. (1987) Int. J. Cancer 39:297-303; and Vegglan et al. (1989) Tumori 75:510-513). FR-α is overexpressed in greater than 90% of ovarian carcinomas (Sudimack and Lee (2000) Adv. Drug Deliv. Rev. 41(2):147-62). In addition, it is also over-expressed in a number of other cancers such as but not limited to breast, colorectal, renal, and lung cancer.
In 1987, Miotti et al. described three new monoclonal antibodies that recognized antigens on human ovarian carcinoma cells (Miotti et al. (1987) Int. J. Cancer 39(3):297-303). One of these was designated MOv18, which recognizes a 38 kDa protein on the surface of choriocarcinoma cells. MOv18 is a murine, IgG1, kappa antibody and mediates specific cell lysis of the ovarian carcinoma cell line, IGROV1. Alberti et al. ((1990) Biochem. Biophys. Res. Commun. 171(3):1051-1055) showed that the antigen recognized by MOv18 was a GPI-linked protein. This was subsequently identified as the human folate binding protein (Coney et al. (1991) Cancer Res. 51(22):6125-6132). Tomassetti et al. showed that MOv18 recognizes a soluble form and a GPI-anchored form of the folate binding protein in IGROV1 cells (Tomassetti et al. (1993) FEBS Lett. 317(1-2):143-146). Subsequent work combined the variable regions of the mouse MOv18 with human IgG1 (kappa) constant region to create a chimerized MOv18 antibody. The chimerized antibody mediated higher and more specific lysis of IGROV1 cells at 10-100 fold lower antibody concentrations (Coney et al. (1994) Cancer Res. 54(9):2448-2455).
U.S. Pat. No. 5,952,484 describes a humanized antibody that binds to a 38 kDa protein (FR-α). The antibody was named LK26, after the antigen by the same name. The original mouse monoclonal antibody was described by Rettig in European Patent Application No. 86104170.5 (published as EP0197435 and issued in the U.S. as U.S. Pat. No. 4,851,332).
Ovarian cancer is the major cause of death due to gynecological malignancy. Although chemotherapy is the recommended treatment and has enjoyed some success, the 5-year survival term is still less than 40%.
A difficult problem in treating ovarian cancer as well as other cancers with cytotoxic drugs is that often the cytotoxin causes toxicity to normal tissues as well as cancerous tissues. An approach to get better specificity to treat cancer is the use of antibodies that can target specific antigens expressed in cancer cells that are not expressed or are expressed at a lower level on normal cells. These targets can be exploited using antibodies to kill antigen-bearing tumors by inhibiting the biological activity of the antigen, eliciting an immune effector function by complement dependent cytotoxicity (CDC) and/or antibody dependent cellular cytotoxicity (ADCC); or by delivering immuno- or radio-conjugates that when delivered to the antigen-bearing cells, specifically kill the target cell. Finding antibodies that can specifically bind to and effectively kill antigen-bearing tumor cells has proven difficult for many cancers. This has been due in part to the inability to obtain robust killing due to lack of immune-effector function or to lack of efficient internalization of antibodies carrying immunotoxins. FRA offers an opportunity to get tumor-specific targeting for several cancer types including ovarian, renal, colorectal and lung cancer.
Provided herein are in-out anti-FRA antibodies that can in the alternative (i.e., have the ability to do both but only one at a time) elicit a robust immune-effector function on and internalize in FRA-positive cells, for example, for delivering toxic conjugates to FRA-positive cells. The antibodies of the invention are effective therapies for cancers that bear FRA such as but not limited to ovarian, renal, colorectal, breast and lung cancers.